U.S. patent number 7,807,728 [Application Number 11/793,494] was granted by the patent office on 2010-10-05 for method for recycling recovered polycondensation polymer.
This patent grant is currently assigned to Asahi Kasei Chemicals Corporation. Invention is credited to Muneaki Aminaka, Ken Someya, Hiroshi Yokoyama.
United States Patent |
7,807,728 |
Yokoyama , et al. |
October 5, 2010 |
Method for recycling recovered polycondensation polymer
Abstract
Disclosed is a method for recycling a recovered polycondensation
polymer which comprises a process wherein a recovered
polycondensation polymer is supplied in a molten state to a
polymerizer having a porous plate, and then after ejecting the
polycondensation polymer through pores of the porous plate, the
polymerization degree of the polycondensation polymer is increased
under a reduced pressure or in a reduced inert gas atmosphere while
dropping the polycondensation polymer along a supporting body.
Inventors: |
Yokoyama; Hiroshi (Okayama,
JP), Aminaka; Muneaki (Okayama, JP),
Someya; Ken (Kurashiki, JP) |
Assignee: |
Asahi Kasei Chemicals
Corporation (Tokyo, JP)
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Family
ID: |
36601693 |
Appl.
No.: |
11/793,494 |
Filed: |
December 19, 2005 |
PCT
Filed: |
December 19, 2005 |
PCT No.: |
PCT/JP2005/023275 |
371(c)(1),(2),(4) Date: |
June 21, 2007 |
PCT
Pub. No.: |
WO2006/068093 |
PCT
Pub. Date: |
June 29, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080146685 A1 |
Jun 19, 2008 |
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Foreign Application Priority Data
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Dec 21, 2004 [JP] |
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2004-369397 |
Aug 16, 2005 [JP] |
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2005-235816 |
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Current U.S.
Class: |
521/40; 422/620;
264/37.1; 528/480; 528/503; 528/502C; 521/40.5; 425/130;
528/502R |
Current CPC
Class: |
C08J
11/04 (20130101); C08G 63/78 (20130101); Y02W
30/62 (20150501); C08J 2367/02 (20130101); Y02P
20/143 (20151101) |
Current International
Class: |
C08J
11/04 (20060101) |
Field of
Search: |
;521/48,48.5,40,40.5,41,42 ;528/272,271,300,301,480,502R,502C,503
;264/37.1 ;425/130,205 ;422/129,131,133,135,245.1,195,196,197 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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48-8355 |
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Mar 1973 |
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JP |
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53-17569 |
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Feb 1978 |
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JP |
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58-96627 |
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Jun 1983 |
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JP |
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63-46089 |
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Sep 1988 |
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JP |
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4-58806 |
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Sep 1992 |
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JP |
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2003-119266 |
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Apr 2003 |
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JP |
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2003-147121 |
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May 2003 |
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JP |
|
2004-224895 |
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Aug 2004 |
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JP |
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2004-323664 |
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Nov 2004 |
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JP |
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2005-2197 |
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Jan 2005 |
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JP |
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99/65970 |
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Dec 1999 |
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WO |
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WO 02/40569 |
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May 2002 |
|
WO |
|
Other References
English language abstract of Taiwanese Patent Publication No.
459004B, published on Oct. 11, 2001. cited by other .
Taiwanese Patent Office Action, mailed Mar. 5, 2008 and issued in
corresponding Taiwanese Patent Application No. 09720123850. cited
by other .
International Search Report for PCT/JP2005/023275 mailed Mar. 20,
2006. cited by other.
|
Primary Examiner: Choi; Ling-Siu
Assistant Examiner: Tischler; Frances
Attorney, Agent or Firm: Staas & Halsey LLP
Claims
The invention claimed is:
1. A process for recycling recovered polycondensation polymer
products, comprising supplying a recovered polycondensation polymer
in a molten state having a changing input viscosity to a
polymerization vessel having a porous plate, ejecting the recovered
polycondensation polymer through pores of the porous plate,
dropping the recovered polycondensation polymer through the
polymerization vessel along a support, and increasing a
polymerization degree of the recovered polycondensation polymer in
the polymerization vessel under reduced pressure or in an inert gas
atmosphere under reduced pressure; wherein melt viscosity of the
recovered polycondensation polymer is continuously measured as the
recovered polycondensation polymer is being supplied to the
polymerization vessel, the reduced pressure in the polymerization
vessel is continuously adjusted based on the melt viscosity to
accommodate the changing input viscosity of the recovered
polycondensation polymer, and the melt viscosity is measured
upstream from the polymerization vessel.
2. The process according to claim 1, wherein the recovered
polycondensation polymer is supplied to the polymerization vessel
as a mixture of the recovered polycondensation polymer and an
unused polycondensation polymer and/or an intermediate polymer, and
the mixture is ejected from the pores of the porous plate.
3. The process according to claim 1, wherein the recovered
polycondensation polymer has a number average molecular weight of
20,000 to 100,000 after increasing the polymerization degree.
4. The process according to claim 1, wherein impurities are
filtered out with a filter positioned at an upstream side of the
porous plate in a channel for the molten-state of the recovered
polycondensation polymer.
5. The process according to claim 1, wherein the recovered
polycondensation polymer is supplied to the polymerization vessel
alone or as a mixture of the recovered polycondensation polymer and
an unused polycondensation polymer and/or an intermediate polymer,
the process further comprises reacting the recovered
polycondensation polymer or the mixture with a molecular weight
adjuster, prior to supplying the recovered polycondensation polymer
or the mixture to the polymerization vessel.
6. The process according to claim 1, wherein the recovered
polycondensation polymer is a recovered polyethylene terephthalate
resin and ejected from the pores of the porous plate at a
temperature ranging from "a crystal melting temperature-10.degree.
C." to "the crystal melting temperature+60.degree. C.".
7. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 1 to a molding machine in a molten state and
molding the polymer.
8. The process according to claim 2, wherein the recovered
polycondensation polymer has a number average molecular weight of
20,000 to 100,000 after increasing the polymerization degree.
9. The process according to claim 2, wherein impurities are
filtered out with a filter positioned at an upstream side of the
porous plate in a channel for the molten-state of the recovered
polycondensation polymer.
10. The process according to claim 8, wherein impurities are
filtered out with a filter positioned at an upstream side of the
porous plate in a channel for the molten-state of the recovered
polycondensation polymer.
11. The process according to claim 2, wherein the recovered
polycondensation polymer is supplied to the polymerization vessel
alone or as a mixture of the recovered polycondensation polymer and
an unused polycondensation polymer and/or an intermediate polymer,
the process further comprises reacting the recovered
polycondensation polymer or the mixture with a molecular weight
adjuster, prior to supplying the recovered polycondensation polymer
or the mixture to the polymerization vessel.
12. The process according to claim 3, wherein the recovered
polycondensation polymer is supplied to the polymerization vessel
alone or as a mixture of the recovered polycondensation polymer and
an unused polycondensation polymer and/or an intermediate polymer,
the process further comprises reacting the recovered
polycondensation polymer or the mixture with a molecular weight
adjuster, prior to supplying the recovered polycondensation polymer
or the mixture to the polymerization vessel.
13. The process according to claim 10, wherein the recovered
polycondensation polymer is supplied to the polymerization vessel
alone or as a mixture of the recovered polycondensation polymer and
an unused polycondensation polymer and/or an intermediate polymer,
the process further comprises reacting the recovered
polycondensation polymer or the mixture with a molecular weight
adjuster, prior to supplying the recovered polycondensation polymer
or the mixture to the polymerization vessel.
14. The process according to claim 2, wherein the recovered
polycondensation polymer is a recovered polyethylene terephthalate
resin and ejected from the pores of the porous plate at a
temperature ranging from "a crystal melting temperature-10.degree.
C." to "the crystal melting temperature+60.degree.C.".
15. The process according to claim 3, wherein the recovered
polycondensation polymer is a recovered polyethylene terephthalate
resin and ejected from the pores of the porous plate at a
temperature ranging from "a crystal melting temperature-10.degree.
C." to "the crystal melting temperature+60.degree.C.".
16. The process according to claim 4, wherein the recovered
polycondensation polymer is a recovered polyethylene terephthalate
resin and ejected from the pores of the porous plate at a
temperature ranging from "a crystal melting temperature-10.degree.
C." to "the crystal melting temperature+60.degree.C.".
17. The process according to claim 13, wherein the recovered
polycondensation polymer is a recovered polyethylene terephthalate
resin and ejected from the pores of the porous plate at a
temperature ranging from "a crystal melting temperature-10.degree.
C." to "the crystal melting temperature+60.degree.C.".
18. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 2 to a molding machine in a molten state and
molding the polymer.
19. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 3 to a molding machine in a molten state and
molding the polymer.
20. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 4 to a molding machine in a molten state and
molding the polymer.
21. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 5 to a molding machine in a molten state and
molding the polymer.
22. A process for producing a molded article, characterized by
comprising transferring the polymer recycled by the process
according to claim 17 to a molding machine in a molten state and
molding the polymer.
23. A process for recycling recovered polycondensation polymer
products, comprising supplying the recovered polycondensation
polymer in a molten state having a changing input viscosity to a
polymerization vessel having a porous plate, ejecting the recovered
polycondensation polymer through pores of the porous plate,
dropping the recovered polycondensation polymer through the
polymerization vessel along a support, and increasing a
polymerization degree of the recovered polycondensation polymer in
the polymerization vessel under reduced pressure or in an inert gas
atmosphere under reduced pressure; wherein melt viscosity of the
recovered polycondensation polymer is continuously measured as the
recovered polycondensation polymer is being supplied to the
polymerization vessel, the reduced pressure in the polymerization
vessel is continuously adjusted based on the melt viscosity to
accommodate the changing input viscosity of the recovered
polycondensation polymer, the melt viscosity is measured upstream
from the polymerization vessel, and a polycondensation reaction
side-product is exhausted from an exhausting port in the
polymerization vessel for reducing pressure.
24. The process according to claim 1, wherein the recovered
polycondensation polymer products comprise at least one of waste
polymer products and defective polymer products.
25. The process according to claim 1, wherein the recovered
polycondensation polymer is subjected to a crystallization process
before being supplied to the polymerization vessel.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This patent application is based on, and claims priority benefit to
PCT Application No. PCT/JP2005/023275 filed Dec. 19, 2005, Japanese
patent application No. 2004-369397 filed Dec. 21, 2004, and
Japanese patent application No. 2005-235816 filed on Aug. 16, 2005,
the disclosures of which are incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to a process for recycling a
recovered polycondensation polymer.
BACKGROUND ART
A polycondensation polymer represented by polyethylene
terephthalate resin (hereinafter sometimes referred to as "PET
resin"), has excellent features such as heat resistance, weather
resistance, mechanical resistance, and transparency. Using such
features, PET resin has been widely used in fibers and magnetic
tapes as well as beverage containers, preforms for manufacturing
beverage containers, injection molded articles for various uses,
and extrusion molded articles such as package films and sheets.
However, in molding such a polycondensation polymer, a large amount
of debris is produced. For example, defective parts, which are not
used as molded articles, obtained during a molding step such as
burr of a molded article, runner and sprue generated in injection
molding, deckle edge generated in molding sheet and film; and
defective parts, which are not used as products, obtained in a
manufacturing step of a molded article, such as alternative
products in the middle of replacing existing products with the
alternative products, defective bottles such as pinhole bottles,
nonstandard products, purge products until the quality is stable,
and resin pellets. Furthermore, in producing a polycondensation
polymer, a large amount of a defective polycondensation polymer
that is not used as a product is generated. Examples of such a
defective polymer include alternative products in the middle of
replacing existing products with the alternative products,
nonstandard products, and purge products. Moreover, molded articles
on market are recovered as recyclable products. It has been desired
to develop a process for recycling these recovered products from a
recent environmental protection point of view.
For example, attempts have been made to reuse a recovered resin by
compounding a new polyester and a scrap polyester at a point of
time during a polyester production step and returning the scrap
component to a flow of the polyester production step (for example,
see Patent Document 1).
However, a polycondensation polymer such as PET resin has a problem
in that its polymer chain is cleaved once heat is applied thereto,
decreasing in molecular weight. Also, a recovered resin decreases
in molecular weight and thus low in physical properties. Therefore,
it is not preferable to employ it again for its original use. For
this reason, the resin thus recovered is merely used for food
trays, which may be made of a relatively low-molecular weight
material and requires less physical properties.
As one of techniques for continuous melt polymerization of esters,
a method of conducting polymerization while dropping a prepolymer
by gravity from the top of a polymerization reactor. For example,
as a process for producing polyesters, there is a technique to
supply a PET oligomer having an average degree of polymerization of
8 to 12 (corresponding to a limiting viscosity of 0.1 dl/g or less)
at 285.degree. C., drop it by gravity along a cylindrical metal net
put perpendicular inside the reactor and conduct polymerization
with a reduced pressure inside the reactor (see Patent Document 2)
and as a process for producing polyamides or polyesters, there is a
technique to conduct polymerization while dropping a polymer along
a linear support put perpendicular inside a reactor (see Patent
Document 3). See Patent Documents 4 to 7. However, according to the
present inventors' study, it is revealed that even if the above
techniques are used as such, it is not possible to obtain
polyesters having a high degree of polymerization. Further, there
is a problem that since oligomers ejected from a porous plate or
the like are vigorously foamed to foul the surface of the porous
plate or the inner walls of the reactor, so that the fouling is
decomposed and modified to be mixed with the polymer during a long
time operation and so deteriorates the quality of polyester
products. Even if the scrap component having a quality lowered
through a thermal history is returned to the flow during the
polymerization step by these techniques, it is impossible to obtain
polyesters having a high degree of polymerization and also the
resulting polyesters are not practically applicable at all because
of remarkably deteriorated hue of the product.
Furthermore, attempts have been made to reuse a recovered resin as
a raw material by completely decomposing the resin into monomer
units (for example, see Patent Document 8). However, the
depolymerization of a resin into monomer units must be performed in
supercritical conditions in an organic solvent and also requires a
purification step of the crystallization solvent on recovered
monomers. Therefore, cost inevitably increases.
In the circumstances, it has been desired to develop a simple and
inexpensive recycling process for a recovered polycondensation
polymer by increasing the molecular weight of the polymer.
[Patent Document 1] JP-B-63-46089
[Patent Document 2] JP-B-58-8355
[Patent Document 3] JP-A-53-17569
[Patent Document 4] U.S. Pat. No. 3,110,547
[Patent Document 5] JP-B-4-58806
[Patent Document 6] WO 99/65970 A
[Patent Document 7] JP-A-58-96627
[Patent Document 8] JP-A-2003-147121
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a process for
recycling a recovered polycondensation polymer by polymerizing the
polymer with high productivity at a low cost while keeping high
quality.
The present inventors have conducted intensive studies with view
toward solving the aforementioned problems. As a result,
surprisingly, they have found that the aforementioned problems can
be solved by polymerizing a recovered polycondensation polymer in
appropriate conditions while dropping the resin along a support.
Based on the finding, the present invention has been completed.
More specifically, the present invention is as follows.
(1) A process for recycling a recovered polycondensation polymer,
comprising supplying the recovered polycondensation polymer in a
molten state to a polymerization vessel having a porous plate,
ejecting the polymer through pores of the porous plate, and
increasing the polymerization degree of the polycondensation
polymer under reduced pressure or in an inert gas atmosphere under
reduced pressure while dropping the polymer along a support. (2)
The process according to item (1), wherein the recovered
polycondensation polymer is ejected from the pores of the porous
plate together with an unused polycondensation polymer and/or an
intermediate polymer. (3) The process according to item (1) or (2),
wherein the recovered polycondensation polymer with an improved
polymerization degree has a number average molecular weight of
20,000 to 100,000. (4) The process according to any one of items
(1) to (3), comprising continuously measuring the melt viscosity of
the recovered polycondensation polymer or a mixture of the
recovered polycondensation polymer with the unused polycondensation
polymer and/or the intermediate polymer to be supplied to the
polymerization vessel, and continuously adjusting the pressure
reduction degree of the polymerization vessel, based on measurement
results of the melt viscosity. (5) The process according to any one
of items (1) to (4), comprising a step of reacting the recovered
polycondensation polymer or the mixture of the recovered
polycondensation polymer with the unused polycondensation polymer
and/or the intermediate polymer, with any amount of a molecular
weight adjuster, prior to supplying the recovered polycondensation
polymer or the mixture to the polymerization vessel. (6) The
process according to any one of items (1) to (5), wherein the
recovered polycondensation polymer is a recovered polyethylene
terephthalate resin and ejected from the pores of the porous plate
at a temperature ranging from "a crystal melting temperature
-10.degree. C." to "the crystal melting temperature-60.degree. C.".
(7) A process for producing a molded article characterized by
comprising transferring the polymer recycled by the process
according to any one of items 1 to 6 to a molding machine in a
molten state and molding the polymer.
According to the process for recycling a recovered polycondensation
polymer of the present invention, it is possible to increase the
polymerization degree of a recovered polycondensation polymer with
good productivity at a low cost while maintaining high quality.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a polymerization vessel and molding
machine used in the present invention; and
FIG. 2 is a schematic view of another polymerization vessel and
molding machine used in the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The polycondensation polymer of the present invention refers to a
polymer composed of at least one type of monomer having not less
than two condensable functional groups, the monomers being bound
via the binding of the functional groups. The monomers may be
composed of an aliphatic hydrocarbon to which the functional groups
are directly bound or composed of an aromatic hydrocarbon to which
the functional groups are directly bound.
Examples of such a polycondensation resin (polymer) include
polymers having a structure in which aliphatic hydrocarbon groups
are bonded via the functional groups, such as an aliphatic
polyester, aliphatic polyamide and aliphatic polycarbonate;
polymers having a structure in which an aliphatic hydrocarbon group
and an aromatic hydrocarbon group are bonded via the functional
groups, such as an aliphatic/aromatic polyester, an
aliphatic/aromatic polyamide, and an aliphatic/aromatic
polycarbonate; and
polymers having a structure in which aromatic hydrocarbon groups
are bonded via the functional groups, such as an aromatic polyester
and an aromatic polyamide.
The polycondensation resin mentioned above may be a homopolymer or
a copolymer, or alternatively, a copolymer having different bonds
such as an ester bond, amide bond, and carbonate bond arranged at
random or en bloc. Examples of such a copolymer include polyester
carbonates and polyester amides.
Examples of aliphatic/aromatic polyester include a PET resin. The
PET resin used in the present invention is preferably composed of
ethylene terephthalate repeating units in a content of no less than
50% by mole. In other words, the PET resin may be composed of one
or more other copolymer components in a content of less than 50% by
mole.
Examples of such a copolymer component include
monomers capable of forming an ester such as 5-sodium
sulfoisophthalic acid, 3,5-dicarboxylic acid benzenesulfonate
tetramethyl phosphonium salt, 2,6-nephthalene dicarboxylic
acid,
1,3-butanediol, 1,4-butandiol, neopentyl glycol, 1,6-hexamethylene
glycol, 1,4-cyclcohexane diol, 1,4-cyclohexane dimethanol,
isophthalic acid, oxalic acid, succinic acid, adipic acid,
dodecanoic diacid, fumaric acid, maleic acid, and 1,4-cyclohexane
dicarboxylic acid; and polyethylene glycol; polypropylene glycol;
polytetramethylene glycol; and copolymers thereof.
The PET resin of the present invention may contain, other than, the
PET resin, a ring-form or linear oligomer, a monomer such as
dimethyl terephthalate (hereinafter simply referred to as "DMT"),
terephthalic acid (hereinafter simply referred to as "TPA") and
ethylene glycohol (sometimes simply referred to as "EG"); various
types of additives; and other resins.
The present invention is directed to a process for producing a
high-quality polycondensation polymer by supplying a recovered
polycondensation polymer in a molten state to a polymerization
vessel, thereby increasing a polymerization degree.
The recovered polycondensation polymer used herein refers to
defective products including alternative products in the middle of
replacing existing products with the alternative products and resin
pellets generated in a polymerization step;
burr, runner, gate, sheet and film edge generated in a molding step
of a polycondensation polymer;
a massive resin generated in a step from start-up to a stabilized
state, and nonstandard molded articles generated;
defective products such as pinhole bottles generated in a
production step;
containers recovered for recycling such as used PET bottle waste;
and
recycling flakes of used PET bottle waste produced by sorting,
washing and shattering used PET bottle waste.
Since a polycondensation polymer such as PET resin is depolymerized
by application of heat and reduced in molecular weight, a recovered
resin product cannot be reused for its original purpose even if it
is melted again. However, if a recovered polycondensation polymer
reduced in molecular weight is polymerized to increase the
molecular weight, the polymer thus obtained can be used as a
product. In addition, this attempt is preferable from both economic
and environmental points of view.
The present inventors have conducted studies under the
aforementioned circumstances and found that a polycondensation
polymer of a high polymerization degree can be obtained by
supplying a recovered polycondensation polymer in a molten state to
a polymerization vessel having a porous plate, ejecting the molten
polymer from the pores of the porous plate, increasing a
polymerization degree of the polycondensation polymer under reduced
pressure or in an inert gas atmosphere under reduced pressure while
dropping it along a support, and continuously taking out the
resultant polymer from the polymerization vessel.
The temperature during polymerization performed in a polymerization
vessel according to the present invention preferably ranges from
"the crystal melting point of a recovered polycondensation
polymer-10.degree. C." to "the crystal melting point+60.degree.
C.".
In the case of recovered PET resin, the PET resin of a high
polymerization degree can be obtained by supplying recovered PET
resin to a polymerization vessel in a molten state, ejecting it
from the pores of the porous plate at a temperature ranging from
"the crystal melting point of the resin-10.degree. C." to "the
crystal melting point+60.degree. C.", preferably from "the crystal
melting point-5.degree. C." to "the crystal melting
point+40.degree. C.", and further preferably, from "the crystal
melting point+1.degree. C." to "the crystal melting
point+30.degree. C.", increasing the polymerization degree of the
resin under reduced pressure, while dropping along a support, and
continuously taking out from the polymerization vessel.
In the present invention, when a recovered polycondensation polymer
is introduced into a polymerization vessel, it is preferable that
the polymer is sorted if necessary, shattered, washed, dried,
melted and introduced into the polymerization vessel of the present
invention. It is also preferable that the recovered polymer is
crystallized before dried to avoid melt-solidification. To attain
this, if necessary, an extruder and/or a preparatory melting vessel
may be arranged upstream of the polymerization vessel of the
present invention with a crystallization apparatus, sorting
apparatus, shattering apparatus, washing apparatus, and dryer
interposed between them. As the extruder, use may be preferably
made of the one that melts and supplies a resin. An extruder may be
appropriately chosen from those having a single screw, double
screw, a rotatable screw in the same direction, and a rotatable
screw different directions. As the dryer, use is preferably made of
the one that can be removed a moisture content as much as possible
to avoid a decrease of the polymerization degree in melting. More
specifically, use may be preferably made of a dryer using hot-air
flow or inert gas flow, or a vacuum dryer. As the temperature of a
dryer, any temperature is acceptable as long as oxidation and heat
deterioration can be avoided, and preferably 180.degree. C. or
less.
In particular, a low crystalline state of a recovered PET resin is
developed by abruptly cooling when a molded article or a molten
resin is taken out in some cases. In other cases, melt
solidification of resin pieces is developed by abruptly heating
when it is dried. When melt-fusion takes place, feeding of a resin
by an extruder is inhibited. Therefore, the resin is preferably
crystallized in advance by heating it to the melting temperature or
less.
A recovered polycondensation polymer is supplied in a molten state
from a preparatory melting vessel and/or an extruder to a
polymerization vessel according to the present invention. If
necessary, it may be supplied via a filter.
A recovered polycondensation polymer may be supplied singly to a
polymerization vessel according to the present invention for
recycling. Alternatively, a recovered polycondensation polymer may
be supplied together with an unused polycondensation polymer and/or
an intermediate polymer to a polymerization vessel according to the
present invention, for recycling. The unused polycondensation
polymer used herein refers to unused resin pellets that have not
been used for molding since they were produced, or an unused
polycondensation polymer in a molten state produced and taken out
from a molten polymerization vessel. Furthermore, the intermediate
polymer used herein refers to a polymer of the initial
polymerization stage having a low polymerization degree compared to
the polycondensation polymer used as a product, and may contain an
oligomer and a monomer. A recovered polycondensation polymer can be
mixed with these unused polymerization condensation polymer and/or
an intermediate polymer, supplied to the preparatory melting vessel
and/or extruder, and introduced into a polymerization vessel
according to the present invention in a molten state.
Alternatively, use may be preferably made of a process for
improving handleability and controlling the polymerization degree
and productivity of a recycled product by reacting a recovered
polycondensation polymer or a mixture of a recovered
polycondensation polymer and an unused polycondensation polymer
and/or an polymer intermediate polymer, with any amount of a
molecular weight adjuster, in any step before supplying the
recovered polycondensation polymer or the mixture to a
polymerization vessel according to the present invention.
Next, a step of polymerizing a recovered polycondensation polymer
in a polymerization vessel according to the present invention will
be explained.
The polymerization degree of a recovered polycondensation polymer
or a mixture of a recovered polycondensation polymer and an unused
polycondensation polymer and/or an intermediate polymer suitable
for supplying to a polymerization vessel according to the present
invention can be defined by a melt viscosity when the viscosity is
evaluated at a temperature of polymerization carried out in the
polymerization vessel of the present invention, at a shear rate of
1000 (sec.sup.-1). The melt viscosity preferably ranges from 60 to
100,000 poises. When the melt viscosity is set at 60 poises or
more, it is possible to suppress vigorous foaming and scattering of
an intermediate polymer ejected from pores of a porous plate of the
polymerization vessel. When the melt viscosity is set at 100,000
poises or less, a reaction side-product can be efficiently removed
out of the system, facilitating polymerization without a problem.
More preferably, the melt viscosity ranges from 100 to 50,000
(poise), further preferably, 200 to 10,000 poise, and most
preferably, 300 to 5,000 (poise). In the present invention, it is
preferable that an intermediate polymer has such a relatively high
viscosity. This is because a resin can be polymerized while
containing a large amount of foams, with the result that the
polymerization rate can be greatly increased.
When a recovered polycondensation polymer is PET resin, a
polymerization degree preferably falls within the range of 0.40 to
1.20 dl/g in terms of an intrinsic viscosity [.eta.], which is used
generally for expressing viscosity.
In the present invention, to manufacture a recycled product in high
quality, it is important to suppress a molten-state of the
recovered polycondensation resin ejected from the pores of a porous
plate from vigorous foaming and scattering in a polymerization
vessel according to the present invention. When the recovered
polycondensation polymer is ejected at the aforementioned
temperature, scattering of the recovered polycondensation polymer
caused by vigorous foaming can be suppressed and a polymerization
reaction side produce is removed outside the system, with the
result that a polycondensation reaction can be performed
efficiently.
When the resin ejected from the pores of a porous plate is
vigorously foamed and scattered, the scattered resin is adhered to
and smears the mouth ring surface and wall surfaces of the porous
plate for ejection. The attached resin, if it retains for a long
time, is decomposed with heat and produces a colored low molecular
weight material or a degradation product. If a desired resin is
contaminated with such a material, the resin decreases in quality
and fails to acquire a desired polymerization degree.
To prevent scattering of a resin (PET resin) caused by vigorous
foaming, it is preferable that the intrinsic viscosity [.eta.] of a
recovered polymer that is to be supplied to a polymerization vessel
according to the present invention, is adjusted to not less than
0.40 dl/g. On the other hand, to remove efficiently a
polycondensation reaction side-product such as EG from the system
and to drop the resin while maintaining proper foaming for
improving the polymerization degree, it is desirable to reduce the
intrinsic viscosity of the recovered resin. The intrinsic viscosity
of the recovered resin is preferably 1.20 or less, further
preferably 0.50 to 1.00 dl/g, and more preferably 0.60 to 0.90
dl/g.
To obtain high-quality PET while suppressing foaming by imparting
an appropriate viscosity and while preventing coloration due to
heat decomposition, it is preferable that the ejection temperature
of the recovered PET resin is set at not more than "a crystal
melting point+60.degree. C.". On the other hand, to uniformly eject
the molten resin from a porous plate and drop the resin along a
support while maintaining a uniform molten state, the ejection
temperature is preferably set at not less than "a crystal melting
point of the recovered resin-10.degree. C.", more preferably, from
"the crystal melting point-5.degree. C." to "the crystal melting
point+40.degree. C.", and further preferably from "the crystal
melting point+1.degree. C." to "the crystal melting
point+30.degree. C.". Generally, the crystal solidifying point of a
polymer is considerably lower than the crystal melting point. In
particular, the crystal solidifying point of a resin having a low
crystallinity falls over several ten degrees. Since a polyethylene
terephthalate resin does not have good crystallinity, it can be
handled at a temperature lower by 10.degree. C. from the crystal
melting point.
Note that the crystal melting point is defined by a peak
endothermic temperature due to melting of a crystal measured by an
input compensation type differential calorimeter, Pyris 1 DSC
((trade name, manufactured by Perkin Elmer Inc.) in the following
conditions. The peak temperature was determined by use of the
analysis software attached thereto.
Measuring temperature: 0 to 300.degree. C.
Temperature raising rate: 10.degree. C./min.
The ejection temperature is preferably from "a crystal melting
point-10.degree. C." to "the crystal melting point+60.degree. C.",
more preferably, from "the crystal melting point-5.degree. C." to
"the crystal melting point+40.degree. C.", and further preferably,
from "the crystal melting point+1.degree. C." to "the crystal
melting point+30.degree. C.". In particular, to reduce the content
of impurities such as acetoaldehyde, polymerization is desirably
performed at as a low temperature as possible.
The porous plate for use in ejecting a recovered polycondensation
polymer is a plate-form member having a plurality of through-holes.
The thickness of the porous plate is not particularly limited;
however, generally ranges from 0.1 to 300 mm, preferably 1 to 200
mm, and further preferably, 5 to 150 mm. The porous plate must
withstand the pressure given by a recovered polymer supply chamber
containing molten-state polymer; at the same time, have a strength
for supporting the weight of a support and recovered polymer that
falls along the support, in the case where the support of a
polymerization chamber is immobilized to the porous plate. It is
also preferable that the porous plate is reinforced by a rib or the
like.
The shape of pores of the porous plate may be selected generally
from circular, ellipsoidal, triangular, slit-form, polygonal, and
star shapes. The sectional area of a pore generally falls within
the range of 0.01 to 100 cm.sup.2, preferably 0.05 to 10 cm.sup.2,
and particularly preferably 0.1 to 5 cm.sup.2. The porous plate may
have a nozzle or the like connected to the pore(s). The interval
between pores falls generally within the range of 1 to 500 mm, and
preferably 25 to 100 mm in terms of the distance between the
centers of pores. The pores of the porous plate may be
through-holes or tubes attached thereto, and alternatively, a
tapered form. It is preferable to set the size and shape of pores
such that a pressure loss of a molten recovered PET resin, when it
passes through the porous plate, falls within the range of 0.1 to
50 kg/cm.sup.2.
The material of the porous plate is generally and preferably a
metallic material such as stainless steel, carbon steel, hastelloy,
nickel, titanium, chromium and other alloys.
Furthermore, it is preferable to set a filter in a channel for a
molten-state recovered polymer at the upstream side of the porous
plate. Foreign matter clogging the pores of the porous plate can be
removed by the filter. The type of filter is appropriately set so
as to remove foreign matter equal to and larger than pore sizes of
the porous plate and so as not to be broken by a recovered polymer
passing therethrough.
Examples of a process for ejecting a recovered polymer through such
a porous plate, include a process for dropping a recovered polymer
by use of a liquid head or its own gravity, and a process for
pressurizing and extruding a polymer by a pump. Use may be
preferably made of a process for extruding a polymer by a pump such
as a measurable gear-pump in order to suppress quantitative
variation of a falling recovered polymer.
The number of pores of the porous plate is not particularly limited
and may be varied depending upon the conditions such as reaction
temperature and pressure, the amount of a catalyst and the
molecular weight range of the polymer to be polymerized. Generally,
when a polymer is produced in an amount of, for example, 100 kg/hr,
5 to 105 pores are required.
The recovered polymer ejected from the pores of the porous plate
must be polymerized under reduced pressure while dropping it along
a support. At this time, it is preferable that there is a portion
where foams are generated without being burst immediately upon
generation. More specifically, foams are desirably generated at the
place on which the resin falling along a support is landed. As
Examples of such a support include a wire-form, chain-form or a
lattice (grid)-form made of wire materials in combination, a cubic
lattice-form made of wire material in the shape of a jungle gym, a
flat or curved thin-film, a porous plate, and a tower formed by
stacking regular fillers or irregular fillers.
To efficiently extract a polycondensation reaction side-product
such as EG and also reduce the content of impurities such as
acetaldehyde in a recycled polymer, it is preferable that the resin
drops have a large surface area. For this reason, the support
preferably has a wire-form, chain-form, lattice-form or cubic
lattice form. To more efficiently extract a polycondensation
reaction side-product such as EG, thereby increasing a
polymerization rate, and further reduce the content of acetaldehyde
in a recycled polymer, other than increasing the surface area, it
is particularly preferable that a recovered polymer is dropped
along a support having projections and depressions on the way on
which a recovered polymer falls. This is because the polymer is
actively stirred by the projections and depressions, thereby
renewing the surface of the polymer. For this reason, the structure
of the support is particularly preferably a chain form, cubic
lattice form, and wire form having projections and depressions,
that is, structural obstacles inhibiting the drop of a resin, on
the way on which a resin falls. As a matter of course, it is one of
the preferable approaches that these supports are used in
combination.
The wire form used herein refers to a solid material having an
extremely large ratio of the sectional area based (calculated from)
on an average length of outer circumference of the section to the
length in perpendicular to the sectional area. The sectional area
is not particularly limited; however generally ranges from
10.sup.-3 to 10.sup.2 cm.sup.2, preferably from 10.sup.-2 to
10.sup.1 cm.sup.2, and particularly preferably, 10.sup.-1 to 1
cm.sup.2. The shape of the section is not particularly limited;
however, generally selected from circular, ellipsoidal, triangular,
square, polygonal, star shape and others. The shape of the section
may or may not change lengthwise. The wire may be a hollow
body.
The wire may be made of a single filament or a plurality of
filaments combined, for example, by twisting. The surface of the
wire may be smooth, rough and bumpy in part. The material of wire
is not particularly limited; however generally selected from
stainless steel, carbon steel, hastelloy, titanium and the like.
Various surface treatments such as plating, lining, passive-state
processing, and acid washing may be applied to the wire, if
necessary.
The lattice (grid) form used herein refers to a solid material made
of wire-like filaments in the form of a lattice. The wire filaments
used in combination may be straight or curved. The wire filaments
may be mutually crossed at any angle. In a projection view of the
lattice (grid) form material obtained by vertically projecting
light to the lattice plane, the area ratio of the solid material
and the space is not particularly limited; however generally falls
within the range of 1:0.5 to 1:1,000, preferably 1:1 to 1:500, and
particularly preferably, 1:5 to 1:100. The area ratio in the
horizontal direction is preferably equal; however, that of the
vertical direction is preferably equal or preferably the ratio of
the space increases toward the bottom.
The chain-form used herein refers to a solid material formed by
sequentially connecting the wire rings. The shape of the wire ring
may be circular, ellipsoidal, rectangular and square. Wire rings
may be connected one dimensionally, two-dimensionally, and
three-dimensionally.
The cubic lattice form used herein refers to a solid material
having a three-dimensional lattice form, such as a jungle gym,
formed of wire-like filaments. The wire filaments may be straight
or curved and mutually crossed at any angle.
The "wire form having projections and depression on the way on
which resin falls" refers to a wire filament having rods having a
circular or polygonal sectional shape attached in perpendicular to
the wire filament or a wire filament having disk-form or circular
form solid materials attached thereto. The difference between
projections and depressions is preferably 5 mm or more. Specific
examples of such a wire include a wire filament having disks
attached at intervals of 1 to 500 mm such that the wire filament
passes through the center of the disks each of which has a diameter
larger by 5 mm than that of the wire filament and less than or
equal to 100 mm and a thickness of 1 to 50 mm.
In a chain-form support, a cubic lattice form support and a wire
form support having projections and depressions formed in a
perpendicular direction to the way on and along which the polymer
drops, the volume ratio of the solid portion and space of the
support to be combined is not particularly limited; however,
generally falls within the range of 1:0.5 to 1:10.sup.7, preferably
1:10 to 1:10.sup.6, and particularly preferably 1:10.sup.2 to
1:10.sup.5. The volume ratio in the horizontal direction is
preferably equal, whereas the volume ratio in the vertical
direction is preferably equal or the ratio of the space increases
toward the bottom.
The number of supports, whether or not a single or plural, may be
appropriately chosen depending upon the shape of the support. In
the cases of a wire form and linearly extending chain form, the
number of supports generally ranges from 1 to 100,000, and
preferably 3 to 10000. In the case of lattice form, a
two-dimensional structure such as a two dimensional chain-form,
thin-film form, and porous plate form, the number of supports
generally ranges from 1 to 1,000, and preferably 2 to 100. In the
case of a three-dimensional structure such as a three-dimensional
chain form, cubic lattice form, and a filler tower, the number of
supports may be single or plural. In this case, whether a single
support or a plurality of supports (by splitting) are used can be
appropriately determined in consideration of the size of an
apparatus and installation space, etc.
In the case of a plurality of supports, the supports are preferably
arranged with an appropriate spacer interposed between them to
avoid mutual contact of supports.
In the present invention, a recovered polymer is generally supplied
from at least one pore of the porous plate to a single support. The
number of pores can be appropriately selected depending upon the
shape of the support. Alternatively, a recovered polymer passed
through a single pore can be dropped along a plurality of supports.
However, to obtain a resin having uniform quality by rendering the
dropping conditions uniform, the number of supports along which the
resin is dropped is preferably as small as possible. For this
reason, most preferably, a recovered polymer is supplied from a
single pore to a single support along which the resin (polymer)
drops.
The position of a support is not particularly limited as long as a
recovered polymer can drop along the support. The method of fitting
a support to a porous plate is appropriately selected from the two
cases: one is where a support is arranged to thread through a pore
of the porous plate. The other is where a support is not arranged
to thread through a pore but arranged to below a pore of the porous
plate.
The recovered polymer passed through a pore can be dropped along a
support. The falling of the polymer may start from a height ranging
from preferably 0.5 to 50 m, further preferably, 1 to 20 m and more
preferably, 2 to 10 m.
The flow rate of a recovered polymer to be passed through a pore is
preferably 10.sup.-2 to 10.sup.2 L/hr per pore, and particularly
preferably, 0.1 to 50 L/hr. If the flow rate falls within the
range, the cases where the polymerization rate and productivity
significantly decrease are successfully avoided.
The average time required until completion of dropping of a
recovered polymer along a support preferably falls within the range
of 10 seconds to 100 hours, more preferably 1 minute to 10 hours,
further preferably 5 minutes to 5 hours, and particularly
preferably 20 minutes to 3 hours.
In the present invention, it is necessary to perform polymerization
under reduced pressure while a recovered polymer is dropped along a
support. This is because a polycondensation reaction side-product
such as EG generated with the progress of the reaction is
efficiently removed from the reaction system, thereby facilitating
polymerization. The reduced pressure used herein refers to a
pressure lower than the atmospheric pressure. Generally, the
reduced pressure is preferably 50,000 Pa or less, more preferably
10,000 Pa or less, further preferably 1,000 Pa or less, and
particularly preferably, 100 Pa or less. The lowermost limit is not
particularly limited; however, desirably 0.1 Pa or more, in
consideration of the size (capacity) of an apparatus for use in
reducing the pressure of the system.
Alternatively, as one of the preferably approaches, a small amount
of inert gas having no adverse effect upon the reaction may be
introduced to remove EG and volatile substances, such as
acetaldehyde, generated in the system, by carrying them on the
inert gas under reduced pressure.
The recovered polymer for use in the process for recycling a
polymer according to the present invention may be a mixture of
resins having different polymerization degrees in some cases. When
the polymerization degree of the starting recovered polymer mixture
is extremely one-sided, if the polymerization of the recovered
polymers is continued in predetermined constant conditions, the
polymerization degree of the resultant recycled product may vary
depending upon the polymerization degrees of the starting recovered
polymers. For this reason, to obtain a resin having uniform
quality, it is preferable to change polymerization conditions
employed for a polymerization vessel depending upon the
polymerization degree of the starting material to be introduced
into the polymerization vessel.
The polymerization conditions having an effect upon the
polymerization degree of a recycled product include polymerization
temperature, the reduction degree of pressure, and the feed rate of
a recovered polycondensation polymer to a polymerization vessel. Of
them, the reduction degree of pressure can be most preferably
varied depending upon the introduced resin.
The polymerization degree of a molten resin to be supplied is
desirably evaluated based on the melt viscosity thereof immediately
upstream of a polymerization vessel. The melt viscosity is most
preferably evaluated based on the voltage of a gear pump for
feeding the resin in a molten state. Alternatively, a viscometer
may be preferably installed immediately upstream of the
polymerization vessel. It is desirable to control the reduction
degree of pressure of a polymerization system to change it quickly
depending upon the viscosity thus measured.
Furthermore, polymerization is preferably performed in an inert gas
atmosphere under reduced pressure.
It has been conventionally considered that introduction of an inert
gas into a polymerization vessel is performed to advantageously
facilitate a polymerization reaction by reducing the partial
pressure of a side-product generated during a polycondensation
reaction, thereby shifting the equilibrium. However, since the
amount of the inert gas to be introduced in the present invention
may be extremely small, the effect of improving a polymerization
rate due to the reduction of partial pressure is rarely expected.
Therefore, conventional interpretation cannot fit for explaining
the role of such an inert gas. Based on investigation, the present
inventors surprisingly found, by observation, that the foaming
phenomenon of a molten polymer on the support vigorously takes
place by introduction of an inert gas into a polymerization vessel,
dramatically increasing the surface area of the molten polymer and
extremely improving the surface renewal state. Based on an unknown
theory, it is estimated that the change of the inner state and
surface state of the molten resin is a cause increasing a
polymerization rate.
As an inert gas to be introduced, mention may be made of a gas
having no effect upon a resin, such as coloration, degradation and
decomposition. Preferable examples of such an inert gas include
nitrogen, argon, helium, carbon dioxide and lower hydrocarbon gas,
of course, including a gas mixture thereof. As an inert gas,
nitrogen, argon, helium or carbon dioxide is more preferable. Of
them, nitrogen is particularly preferable in view of
availability.
The amount of an inert gas to be introduced in the present
invention may be extremely small, and preferably fall within the
range of 0.05 to 100 mg per gram of a resin taken from a
polymerization vessel. When the amount of an inert gas is 0.05 mg
or more per gram of a resin taken from a polymerization vessel, a
sufficient foaming state can be obtained. As a result, a
polymerization degree effectively increases. On the other hand,
when the amount is 100 mg or less, the reduction degree of pressure
can be more easily increased. The amount of an inert gas is more
preferable set at 0.1 to 50 mg and particularly preferably 0.2 to
10 mg per gram of a resin taken from a polymerization vessel.
Examples of a process for introducing an inert gas include a
process for directly introducing it into a polymerization vessel; a
process for absorbing and/or incorporating an inert gas into a
recovered polycondensation polymer in advance and then allowing the
inert gas absorbed and/or incorporated to release from the
recovered polycondensation polymer under reduced pressure, thereby
introducing it into a polymerization vessel; and a process using
these processes in combination.
Note that, the "absorbed" used herein refers to a state in which an
inert gas is dissolved in a resin and not present in a gaseous
state, whereas the "incorporated" used herein refers to a state of
an inert gas present in the form of air bubbles. When an inert gas
is present in the form of air bubbles, the smaller the air bubbles,
the more preferable. More specifically, air bubbles preferably have
an average size of 5 mm or less and more preferably 2 mm or
less.
The site of a polymerization vessel through which an inert gas is
directly introduced is desirably away from a porous plate and near
a port from which a resin is taken out. Furthermore, it is
desirable that the site is away from an exhausting line for a
reduced pressure.
On the other hand, as a process for absorbing and/or incorporating
an inert gas into a recovered polycondensation polymer in advance,
mention may be made of a process using a known absorption apparatus
such as a filler-tower form absorption apparatus, stacked-stage
form absorption apparatus, and spray tower absorption apparatus, as
is described in for example "chemical apparatus design/operation
series" No. 2, revised, gas absorption, pages 49-54, (published by
Kagaku Kogyosha Inc. on Mar. 15, 1981); and a process for
introducing an inert gas under pressure into a feed pipe for a
recovered polycondensation polymer in a molten state.
What is the most preferable is a process using an apparatus for
absorbing an inert gas into a recovered polycondensation polymer
melted under an inert gas atmosphere while the molten polymer is
dropped along a support. In this process, an inert gas having a
higher pressure than the inner pressure of a polymerization vessel
is introduced into an apparatus for adsorbing the inert gas. The
pressure of an inert gas is preferably 0.01 to 1 MPa, more
preferably 0.05 to 0.5 MPa, and further preferably 0.1 to 0.2
Pa.
In either case, it is preferable that there is a portion at which
foaming takes place when a resin is dropped along a support. More
specifically, foams are desirably generated at the place on which
the polymer (resin) falling along a support is landed. The state of
foaming used herein refers to both states where bubbles burst and
immediately disappear and where bubbles are maintained.
The temperature for polymerizing a recovered polycondensation
polymer while dropping along a support ranges from "the crystal
melting point of the polycondensation polymer-10.degree. C." to
"the crystal melting point+60.degree. C.". In the case where PET
resin is used as the recovered polycondensation polymer, the
temperature ranges more preferably from "the crystal melting
point-5.degree. C." to "the crystal melting point+40.degree. C.",
further preferably, "the crystal melting point+1.degree. C." to
"the crystal melting point+30.degree. C.". When the temperature is
"the crystal melting point-10.degree. C." or more, the resin can
easily and stably fall without significantly increasing the
viscosity of the resin or solidifying on the way on which the resin
falls. On the other hand, when the temperature is "the crystal
melting point+60.degree. C." or less, a recycled product having
high quality can be easily obtained while suppressing coloration
due to heat decomposition. The temperature of a resin in dropping,
preferably falls within the range mentioned above and differs
within 20.degree. C. from the temperature of the resin (polymer)
ejected from a porous plate. The difference is more preferably
within 10.degree. C., particularly preferably within 5.degree. C.,
and most preferably zero, indicating the same temperature as the
ejection temperature. Such a temperature can be attained by
accurately controlling the temperature of a heater or jacket
arranged on the wall of a polymerization vessel covering a support
and/or a heater or a hot medium added to the interior of a
support.
In the present invention, mention may be made of a process
comprising supplying a recovered polycondensation polymer
continuously, in a molten state, from a raw material supply port to
a polymerization vessel, performing polymerization while dropping
the molten polymer ejected from pores of a porous plate along a
support, and taking out the whole amount of the resin landed
continuously from the polymerization vessel; and a process
comprising circulating part of the landed polymer and returning
again to a step of polymerizing the resin while dropping the resin
along the support. Of them, the process comprising the step of
taking out the whole amount of resin landed is rather preferable.
In the process comprising a step of circulating the landed resin
and back again to a step of polymerizing the resin while dropping
the resin along the support, heat decomposition must be avoid in a
liquid storage portion for storing the landed resin and a
circulation line. Therefore, the time and temperature of the resin
retaining in these places are preferably reduced.
The number average molecular weight of a recycled product improved
in polymerization degree and produced from a recovered
polycondensation polymer by a recycling method according to the
present invention is preferably 20,000 or more in view of
mechanical properties of a molded body formed from the recycled
product, preferably 100,000 or less in view of processability in
molding, particularly preferably 22,000 to 50,000, and more
particularly 24,000 to 45,000 in view of quality of a recycled
product such as mechanical properties, hue and impurity
content.
Furthermore, difference in polymerization degree of resin products
is preferably small.
In a starting material for forming a molded article having stable
quality, a value of Mw/Mn of the resin mixture, which is prepared
by taking the same amount of 10 samples from one lot of products at
random, is preferably 2.6 or less, further preferably 2.4 or less,
and most preferably 2.2 or less.
A recovered polycondensation polymer increased in polymerization
degree can be used directly in a molten state or once formed into
pellets and then melted again for use in molding.
In the case of pellets, the pellets are desirably formed with a
slight loss and extruded uniformly by an extruder. To obtain such
pellets, the molten polymer taken out from a polymerization vessel
is preferably extruded in strand form or sheet form, placed into a
cool medium such as water to cool, and thereafter cut into pellets.
The temperature of the cool medium is preferably 60.degree. C. or
less, more preferably 50.degree. C. or less, and further preferably
40.degree. C. or less. As a cool medium, water is preferably in
view of economy and handling convenience. From this, the
temperature of the cool medium is 0.degree. C. or more. Cutting of
the resin into pellets is preferably performed within 120 seconds
after the resin is extruded and after the temperature is cooled to
100.degree. C. or less.
A recycling process by a molten polymerization process according to
the present invention is advantageous over a process for recycling
a recovered polymer by increasing polymerization degree by solid
phase polymerization. This is because not only a step of forming
pellets from a recovered polycondensation polymer is omitted but
also time and energy required for polymerization can be reduced.
Furthermore, a recycled product has numerous advantages over the
one obtained by the solid phase polymerization process. For
example, the amounts of contaminants such as unfused substances
during a modeling step and fine powder called fisheye causing a
molding failure, are low. The obtained pellets have a low degree of
crystallinity compared to those recycled by the solid phase
polymerization process, so that the deterioration of polymerization
degree due to heat generation caused by shearing during a molding
step and the amount of heat decomposition product such as
acetaldehyde are low. On the other hand, it is extremely difficult
to increase the polymerization degree of the recovered
polycondensation polymer and quality such as hue of the polymer
decreases in the conventional molten polymerization technique.
Therefore, it has been difficult to produce a recycled polymer
excellent in quality like in the present invention.
A recycled polymer increased in polymerization degree by a
polymerization process according to the present invention is used
for molding. At this time, it is important to perform molding while
suppressing a decrease of polymerization, coloration due to heat
decomposition, and generation of volatile low molecular weight
impurities. To attain this, it is preferable that a recycled
polymer is transferred in a molten state from a polymerization
vessel to a molding machine without solidifying and then subjected
to melt molding. The "molten state" refers to a melt and flowable
state of a resin attained by heat application. At this state, the
viscosity of the resin is approximately 500,000 Pas or less.
In the present invention, a recycled polymer excellent in quality
can be manufactured by the polymerization process mentioned above.
In addition, a high-quality molded article, which is an object of
the present invention, can be manufactured with high productivity
by molding the recycled polymer while maintaining the excellent
equality without solidifying. Combination of a recycling process by
a melt-polymerization process according to the present invention
with a process for molding a recycled polymer without solidifying
at any moment is advantageous over a process of recycling a polymer
increased in polymerization degree by a solid-phase polymerization
process, since not only a step of palletizing a recycled product
can be omitted, but also time and energy required for
polymerization can be reduced. In addition, a step of drying
pellets before molding and a step of melting the pellets again for
molding are not required. As a result, energy can be saved and
decomposition of a resin can be prevented.
When the temperature during transferring and molding of a resin is
not less than a crystal melting temperature-10.degree. C., a resin
can be easily and stably transferred and molded without a
significant increase of viscosity and solidification. On the other
hand, when the upper limit of the temperature is a temperature
higher by 60.degree. C. than a crystal melting temperature, it is
easy to obtain a high quality PET molding product while suppressing
coloration due to heat decomposition and generation of low
molecular weight volatile impurity. The temperature is preferable
higher by 1 to 40.degree. C., more preferably higher by 5 to
30.degree. C., and particularly preferably higher by 10 to
20.degree. C. than the crystal melting point of a recycle polymer.
Such a temperature can be attained by appropriately controlling the
temperature of a heater or jacket covering a transfer pipe, a
transfer pump, and a molding machine.
Furthermore, the time is preferably within 40 minutes, more
preferably within 20 minutes, and particularly preferable within 10
minutes. The shorter the time, the more preferable. Note that, the
"time" used herein refers to a period from discharge of a molten
resin from the discharge pump of a polymerization vessel to cooling
of the molten resin to a crystal melting temperature of the resin
or less in a molding machine or outside the molding machine. When a
resin is continuously circulated through a pipe or the like, an
average time calculated from the volume of a pipe and the flow rate
of the resin can be employed. In the case where the time changes,
the operation can be performed within the aforementioned time.
The present invention includes the case where additives such as a
stabilizing agent, (crystal) nucleating agent, pigment are added if
necessary by a single screw or double screw kneader placed between
a polymerization vessel and a molding machine in the conditions of
the aforementioned temperature and time.
The present invention includes the case where various types of
additives such as a delustering agent, thermostabilizer, flame
retardant, antistatistic agent, defoaming agent, color adjuster,
antioxidant, UV-ray absorbing agent, crystal nucleating agent,
whitener, and impurity trapping agent may be copolymerized or added
if necessary. These additives may be added at any time.
In particular, a stabilizer is preferably added in the present
invention. In the case of a recovered polycondensation polymer is
PET resin, a penta valent and/or tri valent phosphorus compound and
hindered phenolic compound are preferable. The addition amount of
such a phosphorus compound is preferably 2 to 50 ppm and more
preferably 10 to 200 ppm in terms of a weight ratio of phosphorus
element contained in PET. As an example of such a phosphorus
compound, use may be preferably made of trimethyl phosphite,
phosphate, and phosphorous acid. Such a phosphorus compound is
preferably used since it suppresses coloration of PET resin and has
the effect of a crystal-nucleating agent.
The hindered phenolic compound is a phenolic derivative having a
sterically hindered substituent at a position in the vicinity of a
phenolic hydroxide group, in other words, a compound having one or
more intramolecular ester bonds. The addition amount of such a
hindered phenolic compound is preferably 0.001 to 1% by weight, and
more preferably, 0.01 to 0.2% by weight relative to the PET resin
obtained.
Examples of such a hindered phenolic compound include
pentaerythritol
tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate),
1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,
Octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and
N,N-hexamethylene bis(3,5-tert-butyl-4-hydroxyhydrocinamide). As a
matter of course, a stabilizer for these compounds may be
preferably used.
The stabilizer may be added in any stage from the beginning to a
molding step. A phosphorus compound is preferably added in the
beginning of a polycondensation reaction and a hindered phenolic
compound is added in the beginning of a polycondensation reaction
or after a polymerized resin is taken out from a polymerization
vessel.
In the present invention, it is further preferable to add a
crystal-nucleating agent. As an example of such a nucleating agent,
use may be preferably made of a phosphorus compound, an organic
acid metal salt, and a powder of a resin such as PET and others.
The addition amount of a nucleating agent to PET is preferably 2 to
1,000 ppm, and more preferably, 10 to 500 ppm. Specific examples
include phosphates such as sodium 2,2'-methylene
bis(4,6-di-t-butylphenyl)phosphate, and sodium
bis(4-t-butylphenyl)phosphate, sorbitols such as
bis(p-methylbenzylidene)sorbitol, and metal element containing
compounds such as bis(4-t-butyl benzoic acid)hydroxyl-aluminium.
Particularly, in manufacturing a preform of a bottle formed by
thermal crystallization of the mouth portion with heat, a
crystal-nucleating agent is preferably used since it accelerates
crystallization, thereby reducing the temperature of thermal
crystallization.
In one of preferable methods of the present invention, a trapping
agent for low molecular weight volatile impurities is added. As the
trapping agent, use may be made of a polymer or an oligomer of a
polyamide and polyester amide, a low molecular weight compound
having an amide group and an amine group. Specific examples include
polymers such as polyamides, for example, nylon 6.6, nylon 6, and
nylon 4.6 and polyethylene imines; a reaction product between
N-phenyl benzene amine and 2,4,4-trimethyl pentene; and Irganox
1098 and Irganox 565 (registered trademark) manufactured by Ciba
Speciality Chemicals Inc. These trapping agents are preferably
added in the stage where a resin is taken out from a polymerization
vessel and transferred to a molding machine.
When a resin taken from a polymerization vessel is transferred to a
molding machine through a pipe, heating the pipe by a heater or
jacket and maintaining the pipe warm are preferable in view of
transferring a molten resin. The temperature for heating and
maintaining the pipe is preferable 230 to 300.degree. C. and
further preferably 240 to 280.degree. C.
Next, a preferable polymerization vessel used in the present
invention will be exemplified and explained with reference to the
accompany drawings.
FIG. 1 shows a polymerization vessel for carrying out a method
according to the present invention. A recovered polycondensation
polymer R such as PET resin is fed in a molten state from a raw
material supply port 3 into a polymerization vessel 1 by way of a
transfer pump 2, introduced into the interior of the polymerization
vessel through a porous plate 4 and falls along a support 6 (a
falling resin is also shown). A viscometer is arranged upstream of
the raw material supply port 3. The interior of the polymerization
vessel is controlled at a reduced pressure corresponding to the
viscosity measured by the viscometer. A gas such as EG distillated
from a recovered PET resin and an inert gas such as nitrogen
optionally introduced from a gas supply port 7 are exhausted from
an exhausting port 8 for reducing pressure. The polymer produced is
discharged from a discharge port by a discharge pump 9. The
polymerization vessel 1 is heated and maintained warm by a heater
or a jacket.
The interior of the polymerization vessel is controlled at a
predetermined reduced pressure. A gas such as EG distilled from a
recovered PET resin and an inert gas introduced are discharged from
exhausting port 8 for reducing pressure. The polymer produced is
continuously discharged from the discharge port by the discharge
pump 9, fed through a transfer pipe and a distributor 10 to
injection molding machines A, B, C (11, 12, 13), in which the
polymer is molded. The transfer pump 2, polymerization vessel 1,
discharge pump 9, transfer pipe and distributor 10 are heated and
maintained warm by the heater or the jacket.
FIG. 2 shows a polymerization vessel for carrying out a method
according to the present invention in the case where an inert gas
absorption apparatus is used. A recovered polycondensation polymer
R such as a recovered PET resin is fed from a raw material supply
port N2 to an inert gas absorption apparatus N10 via a transfer
pump N1, passed through a porous plate N3, introduced into the
interior of the inert gas absorption apparatus N10, and falls along
a support N5 (a falling resin is also shown). The interior of the
inert gas absorption apparatus is controlled at a predetermined
reduced pressure by an exhausting port N7 for reducing pressure.
The recovered PET resin absorbs an inert gas such as nitrogen gas
introduced from an inert gas introduction port N6 while falling,
supplied to the polymerization vessel 1 from the raw material
supply port 3 by way of a discharge/transfer pump N8, and
introduced into the interior of the polymerization vessel through
the porous plate 4 and falls along the support 6 (a falling resin
is also shown). The interior of the polymerization vessel is
controlled at a predetermined reduced pressure. EG produced as a
side-product is exhausted from the exhausting port 8 for reducing
pressure. The polymer produced is discharged from a discharge port
by the discharge pump 9. The polymerization vessel 1 is heated and
maintained warm by the heater or the jacket.
A polymer resin is continuously discharged by the discharge pump 9,
fed through a transfer pipe and a branch switching valve 10 to
molding machines A, B, C (11, 12, 13), in which the polymer is
molded. Three or more molding machines may be connected.
In either method, the resin falling along a support and landing at
the lower portion of the polymerization vessel is discharged from
the discharge port by the discharge pump. At this time, the amount
of the resin accumulated at the lower portion of the polymerization
vessel is preferably as small and constant as possible. In this
manner, the coloration and decrease in polymerization degree due to
heat decomposition can be suppressed and qualitative variation of
the obtained resin can be easily suppressed. The accumulation
amount of a resin can be controlled by adjusting a liquid amount
fed by the transfer pump 2 and discharged by the discharge pump 9
by monitoring the accumulation amount through an observation window
5 or monitoring the accumulation amount by a level meter of a
capacitance type.
The polymerization vessel used in the present invention may have,
but not particularly require, a stirrer at the bottom. Accordingly,
a rotation driving part may be removed from the polymerization
vessel, with the result that polymerization can be performed in the
airtight conditions under high vacuum. Since the rotation driving
part of the discharge pump is covered with the resin to be
discharged, the polymerization vessel is significantly excellent in
sealing effect compared to that having a rotation driving part.
The process of the present invention can be performed in a single
polymerization vessel and may be performed in two or more
polymerization vessels.
Furthermore, a single polymerization vessel is longitudinally or
laterally divided into multiple portions and used as a multiple
stage polymerization vessel.
In the present invention, a step of increasing the molecular weight
of a recovered polycondensation polymer such as a recovered PET
resin so as to acquire a desired high polymerization degree may be
performed exclusively by a polymerization process while dropping
the resin passed through the pores of a porous plate, along a
support; however may be preferably carried out in combination with
other polymerization processes performed, for example, in a stirred
polymerization vessel and a transverse stirred polymerization
vessel. Furthermore, in the case where a recovered polycondensation
polymer is supplied together with an unused polycondensation
polymer and/or an intermediate polymer to the polymerization vessel
of the present invention to form a recycle product, the unused
polycondensation polymer and/or the intermediate polymer may be
produced by another polymerization process using, for example, a
stirred polymerization vessel or a transverse stirred
polymerization vessel.
Examples of the transverse stirred polymerization vessel include
polymerization vessels having a screw, independent vane, single
screw, and double screw, more specifically, a polymerization vessel
described in "Research Report from Research Group of Reaction
Engineering: Reactive processing Part 2", chapter 4. (published by
the Society of Polymer Science, Japan, 1992).
As the stirred polymerization vessel, use may be made of any one of
the stirring vessels described in, for example Chemical Apparatus
Handbook, chapter 11 (edited by the Society of Chemical Engineers,
Japan, 1989). The shape of the vessel is not particularly limited
and vertical and transverse cylindrical vessels may be used in
general. The shape of a stirring vane is not particularly limited
and a paddle shape, anchor shape, turbine shape, screw shape,
ribbon shape, and double vanes may be employed.
A step of producing an unused polycondensation polymer and an
intermediate polymer from a raw material may be performed in a
batch system or a continuous system. In the batch system, the whole
amounts of raw materials and reacting substances are placed in a
reaction vessel. After a reaction is performed for a predetermined
time, the whole amount of the reaction mixture is transferred to a
next reaction vessel. On the other hand, in the continuous system,
raw materials and reacting substances are continuously supplied to
each of the reaction vessels and a reaction product is continuously
discharged. The continuous system is preferable to obtain a large
amount of a recycled polymer uniform in quality.
A material for a polymerization vessel used in the present
invention is not particularly limited and generally selected from
stainless steel, nickel, and glass lining, etc.
A process for transferring a recycled polymer obtained through
polymerization to a molding machine is not particularly limited;
however, generally, a means such as a gear pump and an extruder is
used. The transfer of the polymer to the molding machine may be
continuously or intermittently performed. In either case, transfer
and molding must be performed within the predetermined time as
mentioned above. In the case of intermittent transfer, discharge of
a polymer from a polymerization vessel can be intermittently
performed. However, as shown in FIG. 1, a resin is discharged
continuously from a polymerization vessel and intermittently
transferred to two or more molding machines (three machines in the
figure) by sequentially switching transfer pipes in combination
with a distributor 10 arranged between the polymerization vessel
and the molding machines. Besides these, known apparatuses such as
an apparatus composed of a reservoir and a piston, and a machine
called an accumulator for temporarily storing a resin may be
preferably arranged.
The molding machine used in the present invention refers to an
apparatus for forming a molten resin into a predetermined shape.
Examples of such a molding machine include an extruder,
injection-molding machine, and blow-molding machine. Examples of a
molded article formed by such a molding machine include bottles,
preforms of bottles, films, sheets, tubes, rods, fibers and
injection molded articles of various shapes. Of them, the present
invention is suitably applied to form preforms of beverage bottles.
This is because a beverage bottle needs to have excellent strength
and transparency, and, in the case where a recovered
polycondensation polymer is PET, such a bottle is strongly demanded
to be produced with reduced low molecular weight volatile
impurities, which are represented by acetaldehyde and may have an
adverse effect upon taste and odor of the content of the bottle,
and with high productivity.
EXAMPLES
The present invention will be explained by way of Examples.
Major measurement values shown in Examples were determined as
follows.
<Measurement Method>
(1) Intrinsic Viscosity [.eta.]
Intrinsic viscosity [.eta.] was measured by Ostwald viscometer.
More specifically, intrinsic viscosity was obtained by
extrapolating the ratio of specific viscosity .eta..sub.sp (in
o-chloro phenol at 35.degree. C.) to concentration C (g/100 mL),
.eta..sub.sp/C, to concentration of Zero in accordance with the
following equation:
.eta..fwdarw..times..eta..times..times..times..times. ##EQU00001##
(2) Crystal Melting Point
The crystal melting point was measured by an input compensation
type differential calorimeter (trade name: Pyris 1 DSC,
manufactured by Perkin Elmer Inc.) in the following conditions. The
value of an endothermic peak derived from melting of a crystal was
specified as a crystal melting point. The peak value was determined
by use of the analysis software attached thereto.
Measuring temperature: 0 to 300.degree. C.
Temperature raising rate: 10.degree. C./min.
(3) The Amount of Carboxyl Group at Polymer End
A sample (1 g) was dissolved in 25 ml of benzyl alcohol.
Thereafter, 25 ml of chloroform was added to the resultant mixture,
and subjected to titration with a solution of 1/50N potassium
hydroxide in benzyl alcohol. The amount of a carboxyl group was
obtained by assigning a titration value V.sub.A (ml) and a value
V.sub.0 of a blank where no PET is used, to the following equation:
The amount of carboxyl group (meq/kg)=(V.sub.A-Vo).times.20. (4)
Acetaldehyde Content (Water Extraction Method)
Samples cut into small pieces was subjected to frost shattering
under cooling by liquid nitrogen in a 6700 freezer mill (trade
name, a frost shattering machine manufactured by SPEX) for 3 to 10
minutes to prepare a powder having grain sizes of 850 to 1,000
.mu.m. The powder (1 g), was added together with 2 ml of water to a
glass ample tube. After the air of the tube was replaced with
nitrogen, the tube was sealed tight and heated at 130.degree. C.
for 90 minutes to extract impurities such as acetaldehyde. After
cooling, the ample tube was opened and subjected to gas
chromatographic analysis by use of GC-14B (trade name, Gas
Chromatograph) manufactured by Shimadzu Corporation in the
following conditions:
Column: VOCOL (60 m.times.0.25 mm.phi..times.film thickness 1.5
.mu.m)
Temperature conditions: maintain at 35.degree. C. for 10 minutes,
increase temperature to 100.degree. C. at a rate of 5.degree.
C./minute, and thereafter increase to 100 to 220.degree. C. at a
rate of 20.degree. C./minute
Temperature of inlet: 220.degree. C.
Injection method: Sprit method (sprit ratio=1:30), inject 1.5
.mu.l
Measurement method: FID method
(5) Hue (L Value, b Value) of a Resin Evaluated in the Form of
Solution
A sample (1.5 g) was dissolved in 10 g of
1,1,1,3,3,3,-hexafluoro-2-propanol and subjected to analysis in
accordance with the permeability method using UV-2500PC (trade
name, UV ray-visible light spectrophotometer) manufactured by
Shimazu Corporation. The results were evaluated by use of the
analysis software attached thereto.
(6) Molecular Weight Distribution
To evaluate variation of the polymerization degree of a resin
product with time, a sample was taken every 30 minutes and
dissolved in an eluent, 1,1,1,3,3,3,-hexafluoro-2-propanol (in
which 5 mmol of sodium trifluoro acetate is dissolved) in a
concentration of 1.0 mg/ml to prepare a solution. In Examples and
Comparative Examples below, polymerization was respectively
continuously performed for 5 hours or more. Of the sample solutions
prepared as mentioned above, 10 solutions were arbitrarily chosen
and mixed to prepare a solution mixture, which was subjected to
analysis using IILC-8020GPC (Gel permeation chromatography)
manufactured by Tosoh Corporation in the following conditions. The
analysis results were evaluated by use of the analysis software
attached thereto.
Column: HFIP-606M+HFIP-603 manufactured by Shodex
Column temperature: 40.degree. C.
Injection amount: 30 .mu.l
Measurement method: RI detector, PMMA conversion
<Preform, Molding of Bottle>
In Examples, molding was performed as follows.
Molding machine: SBIII-100H-15, double screw stretch bottle molding
machine manufactured by Aoki Technical Laboratory, Inc.
Temperature of cylinder: 280.degree. C.
Temperature of hot runner nozzle: 290.degree. C.
Injection pressure: 140 kg/cm.sup.2
Temperature of mold: water cool
Weight of preform: 24 g
Content of bottle: 500 mL
<Dehydration and Crystallization of Recycled Pet Resin>
A bottle molded article made of PET was washed, shattered by a
shattering machine, and dried by a hot-air dryer at 120.degree. C.
for 12 hours. The shattered material was then transferred to a
vacuum dryer, replaced with nitrogen, and crystallized at
180.degree. C. for 6 hours.
<Supply of Recovered Pet Resin to Polymerization Vessel>
A single screw extruder was attached to an inlet for recovered PET
of the polymerization vessel shown in FIG. 1 so as to introduce the
molten resin extruded from the extruder into the polymerization
vessel by way of a pipe.
Example 1
Used bottles were recovered, washed and shattered. A molten resin
of the shattered bottles having an intrinsic viscosity [.eta.] of
0.65 dl/g and a crystal melting point of 255.degree. C. was
supplied to the polymerization vessel 1 from the raw material
supply port 3 by the extruder. The molten resin while maintaining
the molten state at 260.degree. C. was ejected from the pores of
the porous plate 4 at a rate of 20 g/minute per pore. The resultant
resin was polymerized under reduced pressure of 105 Pa while
dropping the resin along the support 6 in the atmosphere whose
temperature was adjusted equal to the ejection temperature.
Thereafter, the resin was discharged by the discharge pump 9, fed
through the transport pipe and the distributor 10, to a double
screw stretch blow molding machine. As a result, a hollow product
was obtained. The porous plate used herein had a thickness of 50 mm
and 1 mm-diameter pores linearly arranged at 25 mm intervals in 0.4
lines. The support 6 was a metal grid prepared by attaching wire
filaments (2 mm in diameter and 8 m in length) each to a portion of
the porous plate in a close proximity of each pore so as to
vertically hang down, and then arranging wire filaments (2 mm in
diameter and 100 mm in length) at 15 mm intervals so as to cross
with the wire filaments mentioned above at right angles. As the
material of the support 6, stainless steel was used. The discharge
pump 9 was operated while monitoring the resin through the
observation window 5 so as to accumulate little or nothing of the
resin on the bottom of the polymerization vessel. The retaining
time of the resin in this case was 60 minutes. Note that the
retaining time was calculated by dividing the amount of the resin
present inside the polymerization vessel by the supply amount of
the resin. In this Example, as a molding machine, a double screw
stretch blow-molding machine manufactured by AOKI Technical
Laboratory, Inc. was used alone without other molding machines and
the resin was discharged. A preform formation step to a hollow
product formation step were continuously performed in the molding
conditions: the temperature of a resin: 280.degree. C., the
temperature of a mold: 90.degree. C. at a core side, 130.degree. C.
at the upper side near a cavity, 50.degree. C. at the lower side,
the injection time: 7 seconds, the cooling time: 3 seconds, and the
time required for one cycle: 18 seconds. The results are shown in
Table 1. A prepolymer was appropriately foamed in the
polymerization vessel. The obtained molded article exhibited a high
polymerization degree, good color tone, and a less acetaldehyde
content. Hence, a high-quality hollow product made of PET with a
high polymerization degree was obtained.
Example 2
Polymerization and molding were performed in the same manner as in
Example 1 except that EG was introduced at a rate of 5 ml/min from
a liquid addition apparatus of the extruder and the conditions
shown in Table 1 were employed. The results are shown in Table 1.
The prepolymer in the polymerization vessel was appropriately
foamed. The obtained molded article exhibited a high polymerization
degree, good color tone, and a less acetaldehyde content. Hence, a
high-quality hollow product made of PET with a high polymerization
degree was obtained.
Examples 3 to 5
Polymerization and molding were performed in the same manner as in
Example 1 except that support structures shown in Table 2 were
employed. The results are shown in Table 1. The obtained molded
article exhibited a high polymerization degree, good color tone,
and a less acetaldehyde content. Hence, a high-quality hollow
product made of PET with a high polymerization degree was
obtained.
Example 6
Polymerization was performed in the same manner as in Example 1
except that the conditions shown in Table 1 were employed.
A strand was stretched through water and palletized by a pelletizer
to obtain pellets. The results were shown in Table 1. The obtained
pellets exhibited a higher polymerization degree than the recovered
product, better color tone, and a less acetaldehyde content. Hence,
a high-quality PET resin pellets were obtained.
Examples 7 and 8
Polymerization and palletizing were performed in the same manner as
in Example 6 except that nitrogen was introduced as shown in Table
1. The results are shown in Table 1. In this case, a high-viscosity
PET resin pellets were obtained with good color tone and in a less
acetaldehyde content.
Comparative Example 1
Bottles were washed, shattered, dried and crystallized and
thereafter, directly subjected to double screw stretch blow
molding. The results are shown in Table 1. In Comparative Example
1, it was difficult to mold a bottle since the drawdown of a
preform was significant due to a reduction of molecular weight.
Comparative Example 2
Polymerization and molding were performed in the same manner as in
Example 1 except that transverse double screw polymerization vessel
having a disk-form stirring vanes was used as a polymerization
vessel and the polymerization was performed at 290.degree. C. Note
that the resin retaining time in the polymerization vessel was 2
hours. The results are shown in Table 1. It was difficult to obtain
a recycled polymer having a high polymerization degree. The
obtained hollow molded article was colored yellow and had a large
acetaldehyde content.
Comparative Examples 3 to 5
Bottles were washed, shattered and subjected to polymerization
performed in the same manner as in Example 1 except that the
conditions shown in Table 1 were employed. The results are shown in
Table 1. In Comparative Example 3, the molded article was colored
yellow since the polymerization temperature was excessively high
and showed a high acetaldehyde content. In Comparative Example 4,
the resin was solidified since the polymerization temperature was
excessively low, and thus no polymerization was performed. In
Comparative Example 5, polymerization failed to proceed and
decomposition took place. As a result, the viscosity of a resin
decreased.
TABLE-US-00001 TABLE 1 Recovered products (after dehydration,
crystallization) Amount of Polymerization condition Intrinsic
carboxyl Crystal Polymerization viscosity group melting Support
rate Temperature Pressure Material (dl/g) (meq/kg) (.degree. C.)
temperature structure (kg/h) (.degree. C.) (Pa) Example 1 Bottle
0.65 40 255 1 6.0 255 105 Example 2 Bottle 0.65 40 255 1 6.0 255 65
Example 3 Bottle 0.65 41 255 2 8.0 255 105 Example 4 Bottle 0.65 42
255 3 8.0 255 105 Example 5 Bottle 0.65 43 255 4 8.0 255 105
Example 6 Bottle 0.65 40 255 1 6.0 260 65 Example 7 Bottle 0.65 40
255 1 6.0 260 100 Example 8 Bottle 0.65 40 255 1 6.0 255 65
Comparative Bottle 0.65 40 255 -- -- -- -- Example 1 Comparative
Bottle 0.65 40 255 -- -- 290.dagger. 60 Example 2 Comparative
Bottle 0.65 41 255 1 6.0 340 65 Example 3 Comparative Bottle 0.65
42 255 1 6.0 240 65 Example 4 Comparative Bottle 0.65 43 255 1 6.0
255 Normal Example 5 pressure Properties of molded article Amount
of Polymerization condition Intrinsic carboxyl Acetaldehyde
Nitrogen Foaming Smearing viscosity group content Hue (mg/g) state
state (dl/g) (meq/kg) (ppm) Mw/Mn L Value b Value Example 1 0
.largecircle. .largecircle. 0.82 42 5.8 2.1 97.6 0.51 Example 2 0
.largecircle. .largecircle. 0.80 48 7.2 2.0 97.8 0.50 Example 3 0
.largecircle. .largecircle. 0.81 43 6.9 2.1 97.7 0.50 Example 4 0
.largecircle. .largecircle. 0.82 50 6.5 2.1 97.7 0.49 Example 5 0
.largecircle. .largecircle. 0.82 42 6.3 2.0 97.6 0.48 Example 6 0
.largecircle. .largecircle. 0.98 65 6.8 2.1 97.2 0.52 Example 7 5
.largecircle. .largecircle. 1.08 62 6.9 2.0 97.0 0.58 Example 8 0.5
.largecircle. .largecircle. 0.88 37 8.2 2.0 97.5 0.50 Comparative
-- -- -- 0.50 120 5.9 2.5 97.6 0.52 Example 1 Comparative -- -- --
0.64 145 85 2.1 92.1 1.89 Example 2 Comparative 0 X X 0.68 152 129
2.2 92.6 1.76 Example 3 Comparative 0 -- -- -- -- -- -- -- --
Example 4 Comparative 0 None .largecircle. 0.41 130 125 2.6 97.5
0.50 Example 5 .dagger.: Molten polymerization temperature in
transverse double screw polymerization vessel.
TABLE-US-00002 TABLE 2 Longitudinal side Lateral side Filament
Number of Arrangement Filament Arrangement Shape of diameter Length
filaments intervals Diameter Length intervals support (mm) (m)
(filament) (mm) (mm) (mm) (mm) Support 1 Lattice 2 8.0 4 25 2 100
15 Support 2 Lattice 3 8.0 4 50 .times. 50 3 30 30 Support 3 Chain
3 8.0 4 50 .times. 50 -- -- -- Support 4 Wire 5 8.0 4 50 .times. 50
-- -- --
INDUSTRIAL APPLICABILITY
According to the present invention, it is possible to increase
polymerization degree of a recovered polycondensation polymer with
good productivity at low cost while maintaining high quality.
Therefore, the present invention can be suitably applied as a
material recycling technique.
* * * * *